Until you have access to cPanel and fully understand how the DB works, it would be best to have your pilots register on the site.
Honestly, you would be better off to cut your losses and move directly to phpVMS v7. The version of phpVMS you are using is old and no longer supported. And with newer versions of MySQL/MariaDB, you will have issues. Don't believe everything TFDI is telling you. Since you are new to phpVMS, you should be using the newest version of phpVMS - which is version 7.
Ask TFDI what versions of PHP they offer with their hosting - they should have several versions available. Also ask what version of MySQL/MariaDB they use.